A common type of digestion tank comprises a mixer assembly for agitating the excrements, or mixture of liquid and sludge, which exist in the fluid housing tank. Such applications comprises usually tanks having a depth of 20-25 meters or more and a volume of several thousands of cubic meters, in which excrements, feces, sludge, waste water, or the like is stored and digested in order to extract methane gas and carbon dioxide, for example. The liquid/sludge is kept in movement by agitation in order to not having the sludge to sediment and in order to not causing a dense cake at the surface of the liquid/sludge, and thereto in order to obtain an as homogenous mixture as possible which entail that most possible quantities of various gases may be extracted. It shall be pointed out that other liquids, in industrial applications, may be stored in similar conditions in which agitation takes place at the same time as the process gases are not released to the surrounding air.
Mixer assemblies suitable for use in a digestion tank or the like comprises a motor and a gear box that lowers the rotational speed of the output shaft of the mixer assembly to about 15-30 revolutions per minute. The present invention is directed towards solutions in which the motor and the gear box of the mixer assembly are located above the roof of the fluid housing tank, and in which the output shaft of the mixer assembly is lead into the fluid housing tank via a lead through and thereafter hang down freely straight down into the fluid housing tank without being journalled in the lower end of the output shaft. The output shaft of the mixer assembly, including the propeller units being arranged at different heights of the output shaft, presents a consider-able weight which entail that a great load is applied to or near to the attachment of the output shaft to the gear box and/or at other connections.
In connection with or after some time after the fluid housing tank is erected and/or is started to be used a settlement and/or inclination of the tank takes place as a rule, which entail that the motor and the gear box are inclined in relation to a plumbline. Due to the fact that the length of the output shaft usually is for instance 20 meters problem arises already at an inclination of tenths of a degree. If the mixer assembly is used without having the inclination corrected the output shaft will bend during rotation, which for instance may lead to fatigue of the output shaft that will break and/or lead to that other parts of the mixer assembly and the fluid housing tank will break.
Thus, the angular position of the mixer assembly in relation to the roof of the fluid housing tank must be adjustable. Known solutions comprises a lead through which in its turn comprises two interacting wedge shaped discs, which discs are arranged to be connected to the roof of the fluid housing tank and the mixer assembly, respectively. The wedge shaped discs presents central openings for passing through of the output shaft of the mixer assembly and are furthermore turnably arranged in relation to each other in order to be able to adjust the angular position of the mixer assembly in relation to the fluid housing tank. However, a large problem of this known solution is that the wedge shaped discs may not be rotated in relation to each other when the weight of the mixer assembly rests on them, instead the mixer assembly most be lifted by a crane in order to uncover the lead through and in connection therewith gases will flow out which is harmful for the environment as well as for the maintenance staff.